1. Field of the Invention
This invention pertains to a novel tubular spring and to an assembly formed from the tubular spring which permits the fabrication of lightweight cushions with improved mechanical and fire resistant characteristics. Further, it simplifies the construction of and reduces the cost of spring-containing cushions. The invention is particularly useful in vehicle seating and furniture, such as aircraft and surface transportation seats, crashworthy seats, upholstered chairs, sofas, davenports, lounges, mattresses, exercise mats, mats used to line confinement cells, shipping containers, and other places where a shock-absorbing cushion is needed, and related articles.
2. Description of the Prior Art
A wide variety of spring and seat cushion assemblies incorporating different spring designs are known in the art. Many proposals have been made over the years to simplify seat and related cushion design using alternatives to conventional coil springs. For example, the following issued U.S. patents disclose such spring and cushion designs: U.S. Pat. Nos. 359,070, issued Mar. 8, 1887 to Goewey; 1,266,359, issued May 14, 1918 to Vining; 1,579,074 issued Mar. 30, 1926 to Burton; 1,814,789, issued July 14, 1931 to Dorton; 1,839,656, issued Jan. 5, 1932 to Dorton; 2,202,630, issued May 28, 1940 to Hauber; 2,277,853, issued Mar. 31, 1942 to Kohn; 2,321,790, issued June 15, 1943 to Bass; 2,856,988, issued Oct. 21, 1958 to Herider et al.; 3,167,353, issued Jan. 26, 1965 to Crane; 3,618,144, issued Nov. 9, 1971 to Frey et al.; 3,869,739, issued Mar. 11, 1975 to Klein; 4,059,306 issued Nov. 22, 1977 to Harder, Jr.; 4,060,280, issued Nov. 29, 1977 to Van Log; 4,079,994, issued Mar. 21, 1978 to Kehl; 4,109,959, issued Aug. 29, 1978 to Barecki et al.; 4,147,336, issued Apr. 3, 1979 to Yamawaki et al. 4,171,125, issued Oct. 16, 1979 to Griffiths; 4,174,420, issued Nov. 13, 1979 to Anolick et al.; 4,254,177, issued Mar. 3, 1981 to Eulmer; 4,294,489, issued Oct. 13, 1981 to Anolick et al.; 4,429,427, issued Feb. 7, 1984 to Sklar; 4,502,731 issued Mar. 5, 1985 to Snider.
For the reason of cost, flexible polyurethane foam has been widely employed in cushions used in vehicles and furniture. Many aircraft seat cushions, for example, simply comprise a two-pound slab of polyurethane foam covered with a decorative fabric. When an aircraft cabin containing such cushions is subjected to a fire, the foam is easily ignited with a low power energy source, and when ignited it will sustain flame propagation even after removal of the energy source. The flammable and toxic vapors produced by thermal decomposition of the foam create a very hostile environment for passengers. Even when the polyurethane foam is treated with fire retardants, application of a sustained heating rate of approximately 5 watts/cm.sup.2 to one polyurethane foam seat of a multiple-seat array will produce flame spread and ignition to the adjacent seats in less than one minute. This results in sufficient fire growth to permit flames to inpinge on the aircraft ceiling in less than two minutes. The combustion products of conventional polyurethane foam padding include cyanide gas. This toxic gas induces convulsive reactions that restrict coherent motor responses in the victims, and can rapidly cause death. In addition, the vision obscuring associated smoke can have an adverse impact on any emergency procedures being taken in the aircraft cabin. Further, the accompanying flames will raise the local temperature very quickly to a dangerous level. Less flammable foams have been discovered, but they have not been accepted by the aircraft industry because, for the main reason, they have been unduly heavy (not cost effective in view of the high price of aircraft fuel). In contrast, as will be seen below, cushions made in accordance with this invention have a majority of the volume of the enclosed spaces comprised of harmless air, as opposed to the typical foam filled cushions. The cushions of this invention thus possess far less flammability hazard potential than do those in current usage. Examples of cushion designs representing an alternative to polyurethane foam cushions are found in the following issued U.S. patents: U.S. Pat. Nos. 3,374,032, issued Mar. 19, 1968 to Del Giudice; 3,518,156, issued June 30, 1970 to Windecker; 3,647,609, issued Mar. 7, 1972 to Cyba; 3,833,259, issued Sep. 3, 1974 to Pershing; 3,887,735, issued June 8, 1975 to Laberinil; 4,031,579, issued June 28, 1977 to Larned; and 4,092,552, issued June 6, 1978 to Dougan. Commonly owned 4,463,465, issued Aug. 7, 1984 to Parker et al, discloses a polyurethane seat cushion which is partially covered with a matrix that catalytically cracks flammable gases given off by the polyurethane to less flammable species.
Despite the fact that the art relating to spring and cushion design is a well developed, there exists a need for further improvements in these designs, to simply fabrication, improve cost effectiveness and mechanical characteristics, and to reduce weight and potential hazards from fire.